A group of 42 strains of Yersinia ruckeri were characterized and found to show homogenous
biochemical profiles.
The optimal conditions for in vitro culture of a representative strain of Y. ruckeri were
established. The virulence was increased by passage through fish. A standard method for
infection of rainbow trout (Oncorhynchus mykiss) with Y. ruckeri was devised. As a result
cultures of Y. ruckeri grown on full strength of BHIA for 5 h at 30°C in static conditions were
found to be most suitable for infection by both intraperitoneal injection and immersion.
Virulence of stored cultures was maintained for over 1 year at -20 and/or -70° C and virulence
was not lost after up to six consecutive subcultures. The effect on mortality of susceptibility
of various fish stocks, water temperature and stocking density is described. The size of fish
(between 5 and 60 g) had no effect on virulence.
The injection and immersion protocols were used as in vivo models for the study of the effects
of dietary vitamin E, with both laboratory prepared diets and commercially available diets.
Comparative results of haematological and biochemical parameters, histology, mortality
patterns, serum antibody levels and bacterial recovery from the four dietary groups of fish are
presented.
A comparative in vitro and in vivo study of intra and inter strain vanations among
representatives of the serogroup 1 of Y. ruckeri was performed. Under the conditions used,
some strains were virulent and other avirulent. Results of Western blotting and SDS-PAGE
showed the presence of a heat sensitive factor (HSF), present only in the virulent strains of Y.
ruckeri. To date this is the first putative virulence factor described for Y. ruckeri. Further work
was undertaken in an attempt to characterize the HSF. It appears to be located in the
periplasmic space and to have complex lipid and proteinaceous components. HSF is easily
degraded, and is immunogenic and confers some protection when injected into rainbow trout.
Selective media and detection methods for the HSF, and their potential use in laboratory and
field studies are described.
Date of Award | 1990 |
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Original language | English |
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Awarding Institution | |
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Factors affecting the pathogenicity of Yersinia ruckeri
Nozal, M. D. F. (Author). 1990
Student thesis: PhD